[dev] [st] bold as bright (again)

Some time ago, i submitted a pull request that makes colors bright for bold
text. Most Terminals do that, and some programs rely on this (like
htop). The pull request was rejected unless less people ask for it.

As it seems, i'm still the only one, but i modified the pull request to make
the bold-is-bright behavior optional. Now i try again.

I attached two variants of the pull request, one uses preprocessor directives
(pp.diff), the other not. Maybe i'm less lucky this time :)

greetings
stefan